A recent trend in consumer electronic devices is small, battery operated devices with on-board rechargeable batteries that are recharged by using a small, external charging adapter. These consumer devices can be, e.g., cell phones, personal digital assistants (PDAs), personal stereo devices (e.g., “Walkman”, or MP3 Player), laptop computers, calculators, pagers, etc. Typically, the charging adapters for these devices are wall-plug AC adapters that provide bulk, low-voltage AC or DC charging power to the consumer device for operating the device and/or charging the device's on-board battery. Often, cigarette lighter adapters and similar charging adapters are provided for charging the consumer devices from a car's electrical system.
A typical consumer device charging system comprises a source of charging power, a charging circuit and a rechargeable battery. The charging circuit typically controls the amount of charging current delivered to the consumer device's battery, sensing and adjusting the current according to the battery's state of charge. Often, such charging circuits provide additional power for operating the consumer device while it is connected to charging adapter, dividing available power between battery charging and device operation as required.
Sometimes the charging circuit resides within the consumer device; other times the charging circuit is built into the charging adapter. The practice of putting the charging circuit into the charging adapter can be particularly advantageous for very small consumer devices, as it eliminates circuitry from the consumer device itself. Although such charging circuits are typically very small themselves, they can be large in comparison to other circuitry in consumer devices and the space saved by eliminating them can have a significant effect on the size, complexity and cost of the consumer device.
Usually, the charging adapter plugs into the consumer device by means of a wired connection. Sometimes, a connector or a set of contacts on the exterior of the consumer device is arranged so that the act of placing it into a charging “cradle” establishes a physical/electrical connection for charging the device. In this case, the “cradle” is a part of the charging adapter. Most charging systems for consumer devices require a direct electrical connection of this type between the device to be charged and the charging adapter. Over time, these contacts can become worn, loose or dirty, compromising their physical and/or electrical integrity and making them unreliable.
One scheme for powering and/or charging electrical/electronic devices involves electromagnetically coupled coils. A first coil (or antenna) is disposed within a charging apparatus. A second coil (or antenna) is disposed within the device to be charged. A “transmitting” circuit drives the first coil with an AC waveform. The device to be charged is placed in close proximity to the charging apparatus such that an electro-magnetic field produced by the first coil induces a corresponding AC electrical signal in the second coil. By rectifying the electrical signal in the second coil, a source of charging energy for the device to be charged is realized. In effect, the two coils (or antennae) form a transformer by which electrical power and/or signals can be communicated between the charging apparatus and the device to be charged. Such non-contacting charging systems have also been adapted to provided data communication over the same electro-magnetic coupling that provides the charging energy by modulating the charging signal and/or load impedance.